Decline in male fertility has emerged as a significant global concern, with seminal quality—measured by volume, concentration, motility, viability, and morphology—being a critical determinant of reproductive potential [1]. Environmental and geographical factors, including temperature, air pollution, and altitude, have been implicated in this trend [1-3].

Exposure to high ambient temperatures adversely affects semen quality. A meta-analysis demonstrated that high environmental heat significantly decreases semen volume (SMD = –0.74), sperm concentration (SMD = –1.07), total sperm count (SMD = –1.52), motility (SMD = –1.93), progressive motility (SMD = –1.65), and normal morphology (SMD = –2.41) [2]. Similarly, longitudinal data from China indicated an inverted U-shaped relationship between ambient temperature and semen parameters, with deviations below or above ~13 °C causing significant reductions in concentration, motility, and total sperm count [2].

Air pollution plays a deleterious role in sperm function. Narrative reviews and systematic analyses have consistently reported negative associations between particulate matter (PM2.5/PM10) exposure and semen quality, including lowered sperm count, motility, and morphological integrity—likely mediated via oxidative stress and endocrine disruption [3,4]. A large-scale case–control study in China further quantified these effects, revealing elevated odds ratios for impaired semen quality with increased PM exposure, particularly among urban populations [5].

Altitude-related hypoxia is another environmental variable that impairs male reproductive health. Human observational studies, including military personnel deployed at 5,380 m, have documented decreased sperm count, concentration, motility, viability, and altered hormone profiles attributable to hypobaric hypoxia; these effects were reversible after returning to lower altitude [6]. Short-term hypoxic exposure (e.g., 3 months at 3,600 m) resulted in increased sperm abnormalities, specifically head malformations [7]. Animal and human studies corroborate these findings, showing testicular morphological changes, oxidative damage, sperm DNA fragmentation, and impaired spermatogenesis under chronic hypoxia [8].

In India, semen quality trends reflect global declines. A systematic review reported a temporal decrease in sperm concentration (~–1.27 million/mL/year) and morphology (–1.27%/year) among Indian men between 1979 and 2016 [9]. Additionally, a study in Northeast India found that men from high-altitude areas had significantly worse semen parameters—lower count, motility, and progression—compared to those at low altitude [10].

While existing research links heat, pollution, and hypoxia to semen deterioration, studies directly comparing semen quality across different altitudinal zones within India are limited. Considering India’s diverse topography and widespread male fertility issues, investigating how geography influences semen quality could inform public health strategies.

Therefore, this study aims to compare key semen parameters among healthy men residing in hilly (≥1,500 m) and plain (≤300 m) regions of India. We hypothesize that individuals in hilly regions may exhibit reduced semen quality due to chronic hypoxic stress and associated environmental factors.

Study Design and Setting: This was a cross-sectional, observational study conducted over a period of twelve months, involving male participants from two distinct geographic regions of India: hilly regions (≥1,500 meters above sea level) and plain regions (≤300 meters above sea level).

Study Population: A total of 200 adult males aged between 21 and 45 years were enrolled, with 100 participants each from the hilly and plain regions. Inclusion criteria encompassed individuals with no history of infertility, residing in their respective geographic locations for a minimum of five consecutive years. Exclusion criteria included subjects with known reproductive disorders, history of genitourinary surgeries, current or past use of hormonal therapy, tobacco or alcohol abuse, systemic illnesses affecting reproductive health, and occupational exposure to gonadotoxins.

Sample Collection and Processing: Participants were instructed to abstain from ejaculation for a period of 7 days before semen collection. Semen samples were obtained through masturbation in a sterile container within a designated private room at each facility. Samples were immediately transferred to the laboratory for analysis within 30 minutes of collection, maintaining temperature between 20°C and 37°C during transport.

Semen Analysis: The semen analysis was performed as per the guidelines established by the World Health Organization (WHO), 2021 [11]. Parameters assessed included semen volume (mL), pH, sperm concentration (million/mL), total sperm count (million/ejaculate), motility (progressive, non-progressive, and immotile), vitality (percentage of live sperm), and morphology (normal forms %). Each parameter was evaluated by trained laboratory personnel using standardized protocols and quality control procedures to ensure consistency and reliability.

Statistical Analysis: Descriptive statistics were computed for all semen parameters. Data were expressed as mean ± standard deviation (SD) or median with interquartile range (IQR) as appropriate. Intergroup comparisons between hilly and plain region cohorts were conducted using Student’s t-test, depending on the normality of data distribution. A p-value of less than 0.05 was considered statistically significant. All analyses were performed using SPSS software version 26.0 (IBM Corp., Armonk, NY, USA).

The demographic characteristics of the study population are detailed in Table 1. The two groups, comprising residents from hilly and plain regions respectively, were comparable in terms of mean age, body mass index (BMI), duration of residence, and socioeconomic status. No statistically significant differences were observed across these baseline parameters, ensuring appropriate comparability between the two cohorts.

Table 1: Baseline Characteristics of Study Participants

Comparative analysis of semen parameters revealed significant disparities between the two groups, as presented in Table 2 and Figure 1. Men residing in the plains exhibited overall superior semen quality relative to those from the hilly regions. Specifically, marked differences were observed in semen volume, sperm concentration, total sperm count, and progressive motility, with the plain group consistently demonstrating more favorable outcomes. These findings indicate a potential adverse impact of high-altitude environmental conditions on spermatogenic function and ejaculatory dynamics.

Table 2: Comparison of Semen Parameters between Hilly and Plain Regions

Figure 1: Mean Total Sperm Count in hilly versus plain regions

Although the mean seminal pH remained within physiological limits in both cohorts, the difference between the groups was not statistically significant. However, key functional attributes of spermatozoa—namely total motility, vitality, and morphological normalcy—were significantly better in the plain region group. This suggests that not only the quantity but also the functional and structural integrity of sperm is potentially compromised at higher altitudes.

This study demonstrates that men residing in hilly regions exhibit significantly lower semen quality compared to those in plain regions. These findings align with existing evidence suggesting that hypobaric hypoxia associated with high altitude impairs spermatogenic function and semen parameters. Controlled exposure in humans, such as military personnel stationed at 5,380 m, showed reversible reductions in sperm count, motility, vitality, and morphological normalcy—effects attributed to oxidative and hypoxic stressors [12]. Additionally, trekkers exposed briefly to high-altitude environments exhibited elevated reactive oxygen species (ROS) levels in seminal fluid, reduced antioxidant capacity, and subsequent declines in sperm concentration and motility—paralleling our observations [13].

Mechanistically, hypoxia appears to trigger oxidative damage within the testicular microenvironment, promoting apoptosis of germ cells and disrupting seminiferous architecture [14]. Supplementary laboratory models have confirmed that hypoxic conditions activate hypoxia-inducible factor (HIF)-1 pathways in sperm, increasing autophagy while diminishing vitality—further impairing motility and morphological integrity [15]. Furthermore, hypoxia-induced hormonal disruptions at the hypothalamic–pituitary–gonadal axis may contribute: experimental data reveal decreased testosterone synthesis under hypoxic stress, a known determinant of spermatogenesis [16].

Crucially, the absence of significant differences in baseline parameters (age, BMI, socioeconomic status, duration of residence) eliminates major confounding influences, strengthening the argument that altitude-related environment is the principal variable affecting semen quality. Environmental factors, including increased UV exposure and lower temperatures at altitude, may exacerbate oxidative stress and compound hypoxic damage to sperm cells [12,13]. Though mild elevations in ambient pollutants like PM2.5 may occur at higher elevations, their contributions here are likely secondary to oxygen deprivation.

Our data indicate that both quantitative (volume, concentration) and qualitative (motility, vitality, morphology) semen parameters are compromised in the hilly cohort. These results coherently reflect the pattern seen in both human and animal studies, reinforcing the notion that chronic altitude exposure acts via multiple pathogenic pathways—including redox imbalance, hormonal suppression, and structural gonadal changes—to impair male reproductive health [12–15].

This study adds important region-specific evidence from India’s diverse topography. While a few Indian studies have hinted at altitudinal differences in semen quality [10], our systematic comparison across well-defined altitudinal thresholds (≥1,500 m vs ≤300 m) provides robust data for clinical and public health considerations. The reversibility of these changes—as shown in short-term exposure studies—suggests that hypoxic effects may not be permanent, yet the magnitude of decline observed warrants attention for long-term residents.

Limitations include the cross-sectional design, which precludes causal inference, and the absence of direct measures of oxidative markers or reproductive hormones. Future studies should include oxidative stress biomarkers, hormonal profiles, and potentially genetic adaptations (e.g., HIF pathway variants) that might modulate individual susceptibility to hypoxia. Longitudinal designs tracking changes upon relocation from altitude would also clarify reversibility in Indian cohorts.

Men living in hilly regions of India exhibit compromised semen parameters relative to their plain-region counterparts, likely due to altitude-associated hypoxia and oxidative stress. These findings have potential implications for fertility counseling and environmental health interventions targeting populations in high-altitude zones. Further research integrating mechanistic biomarkers and longitudinal assessments is essential to elucidate the pathways and temporal dynamics underlying these observations.

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